790
FXUS63 KGRR 150517
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
117 AM EDT TUE SEP 15 2026
KEY MESSAGES
- SEVERAL ROUNDS OF SHOWERS AND STORMS TOMORROW
- CHANCES FOR RAIN THROUGH THE WEEK
DISCUSSION
ISSUED AT 258 PM EDT MON SEP 14 2026
- SEVERAL ROUNDS OF SHOWERS AND STORMS TOMORROW
FORECAST REMAINS FAIRLY CONSISTENT. THERE WILL BE TWO ROUNDS OF
SHOWERS TOMORROW. THE FIRST WILL BE EARLY IN THE MORNING. IT WILL
MOVE ACROSS LOWER MICHIGAN FROM THE NORTHWEST AND MOVE EASTWARD WITH
HEAVY RAIN POSSIBLE. SEVERE WINDS NOT EXPECTED BUT THERE IS THE
POTENTIAL FOR STRONGEST STORMS TO OVERPERFORM.
ANOTHER LINE IN THE AFTERNOON AND EVENING WILL TREK ACROSS
SOUTHERN MICHIGAN ALONG THE WARM AIR ADVECTION. THE BEST
INSTABILITY WILL BE IN IN AND OH. HOWEVER, DUE TO THE SIGNIFICANT
PWATS, UPWARDS OF 2 INCHES, CAPE'S UPWARDS OF 1500 J/KG, LAPSE
RATES OF 7 C/KG THROUGH THE MID TO LOW LEVELS ALONG WITH STRONG
LOW LEVEL WIND SHEAR AND THERE WILL BE A CHANCE FOR CONVECTION
ALONG AND SOUTH OF THE I 94 CORRIDOR COULD BECOME STRONG TO
SEVERE. SPC CONTINUES TO HAVE A MARGINAL RISK THROUGH THIS REGION.
- CHANCES FOR RAIN THROUGH THE WEEK
THERE REMAINS SOME QUESTION ABOUT WHERE THE FRONTAL PATTERN
SHIFTS THIS WEEK. IF IT SHIFTS/EXPANDS TO THE NORTH THEN QUITE A
BIT OF SOUTHERN LOWER MICHIGAN COULD RECEIVE MULTIPLE ROUNDS OF
SHOWERS AND STORMS THROUGH THURSDAY. THE ZONAL FLOW WILL KEEP MID
LEVEL MOISTURE OVER THE AREA. IF THERE IS ENOUGH WARM AIR
ADVECTION, ALONG WITH ANY MID LEVEL SHORT WAVE AMPLIFICATION, AND
AREAS COULD RECEIVE PERIODS OF HEAVY RAIN. NAEFS SHOWS A
PROLONGED PERIOD OF ANOMALOUS MOISTURE ALONG THE SOUTHERN HALF OF
LOWER MICHIGAN. LATEST NAEFS PWATS ALONG THE I 96 CORRIDOR COULD
BE AROUND 1.25 INCHES AND INCREASE TO 2 INCHES IN NORTHERN IN.
THIS MOISTURE BOUNDARY REMAINS ENTRENCHED OVER THE AREA THROUGH
THE WEEK AND LATEST ENSEMBLES HAS IT SHIFTING NORTHWARD TOWARDS
THE END OF THE WEEK. IF IT SHIFTS SOUTHWARD, THEN MUCH OF THE
REGION WILL REMAIN DRY.
ANOTHER SYSTEM WILL LIFT INTO THE AREA THIS WEEKEND AND COULD
BRING ADDITIONAL SHOWER AND THUNDERSTORM CHANCES SATURDAY.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 111 AM EDT TUE SEP 15 2026
LATEST TRENDS SUGGEST SHOWERS AND THUNDERSTORMS WILL LARGELY STAY
NORTH OF THE TERMINALS THROUGH 09Z BEFORE DRIFTING SOUTH. MVFR
AND LOWER CONDITIONS ARE POSSIBLE IN ANY SHOWERS AND ISOLATED
THUNDERSTORMS. AHEAD OF THUNDERSTORMS A PERIOD OF LLWS IS EXPECTED
WITH WINDS AROUND 45 KTS AT 2KFT. SHOWERS/STORMS WILL CLEAR THIS
AFTERNOON FROM NORTH TO SOUTH. VFR IS THEN EXPECTED THIS
AFTERNOON/EVENING BEFORE PATCHY FOG/RAIN MAY CAUSE CONDITIONS TO
DETERIORATE THIS EVENING. GIVEN LOW CONFIDENCE WITH THIS PART OF
THE FORECAST BEING AT THE END OF THE WINDOW HAVE KEPT THIS OUT OF
THE TAFS WITH THE 06Z PACKAGE.
MARINE
ISSUED AT 258 PM EDT MON SEP 14 2026
CONDITONS DETERIORATE TONIGHT INTO TUESDAY AS AN APPROACHING SURFACE
LOW DEEPENS INCREASING SOUTHERLY FLOW. ENOUGH OF A SIGNAL FOR 35-40
KNOT GALES EXISTS NORTH OF HOLLAND TO HOIST A GALE WARNING, WITH A
SMALL CRAFT ADVISORY SOUTH OF HOLLAND FOR 22-33 KNOT GUSTS. GALES
PERSIST INTO TUESDAY MORNING WITH CONDITIONS HAZARDOUS TO SMALL
CRAFT CONTINUING INTO TUESDAY NIGHT. WILL ALSO HOIST A BEACH HAZARDS
STATEMENT FROM ALLEGAN COUNTY NORTH FOR WAVES AS HIGH AS 12 FEET.
DUE TO THE REFRACTING WAVES AND STRONG SOUTHERLY FLOW, HAVE
EXPANDED THE BEACH HAZARDS TO INCLUDE VAN BUREN COUNTY. THE
SOUTHERLY FLOW COULD SHIFT JUST ENOUGH THAT WAVES MISS SOUTH
HAVEN, HOWEVER GIVEN LATEST TRENDS, THERE IS ENOUGH CONCERN THAT
WAVES COULD GROW TO THE 3-5 FT RANGE BRINGING A HIGH SWIM RISK.
GRR WATCHES/WARNINGS/ADVISORIES
MI...BEACH HAZARDS STATEMENT THROUGH THIS EVENING FOR MIZ037-043-050-
056.
BEACH HAZARDS STATEMENT THROUGH THIS AFTERNOON FOR MIZ064-071.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EDT THIS AFTERNOON FOR LMZ844-
845.
GALE WARNING UNTIL 8 AM EDT THIS MORNING FOR LMZ846>849.
DISCUSSION...CERU
AVIATION...THOMAS
MARINE...CERU
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